The present invention relates to a low-distortion waveform generating method in which waveform data read out of a memory is D-A converted to obtain a sine wave or similar waveform output. The invention also pertains to a waveform generator which utilizes such a waveform generating method.
A conventional waveform generator of this kind is provided with a memory 12, a D/A converter 13, a low-pass filter 14 and an amplifier 15 as shown in FIG. 1. In the memory 12 there is prestored waveform data of one cycle of a waveform which is to be ultimately obtained. For example, in the case of obtaining a sinusoidal waveform output, waveform data of one cycle of a sine wave is prestored. The waveform data is repeatedly read out of the memory 12 and the read-out waveform data is converted by the D/A converter 13 into an analog signal, which is applied to the low-pass filter 14 to remove a sample clock component. The output signal of the low-pass filter 14 is amplified by the amplifier 15, from which an output waveform is provided.
In the case of obtaining a low-frequency waveform output with the above conventional waveform generator, it is possible to obtain a low-distortion output waveform which is substantially faithful to the waveform desired to be ultimately obtained, because a low-distortion, low-frequency amplifier can be implemented as the amplifier 15. In the case of obtaining a waveform output of as high a frequency as hundreds of kilo-hertz to several mega-hertz or in the case of varying the frequency of the waveform output over a wide band, however, the prior art waveform generator cannot yield a low-distortion output waveform substantially faithful to the waveform desired to be ultimately obtained. This is because it is difficult to implement, as the amplifier 15, a low-distortion high-frequency amplifier or an amplifier capable of producing a low-distortion output over a wide band.